prestressing works specs

BAHRAIN BAY Technical Specifications - Volume 9

Bridge Works

RI4326-D017-R3-0029 15 of 82 18 October 2007

4 PRESTRESSING

4.1 GENERAL

4.1.1 Description

This work shall consist of prestressing precast or cast-in-place concrete by furnishing, placing, and tensioning of prestressing steel in accordance with details shown on the Drawings, and as specified in these Specifications and the Contract Documents. It includes prestressing by either the pretensioning or post-tensioning methods or by a combination of these methods.

This work shall include the furnishing and installation of any appurtenant items necessary for the particular prestressing system to be used, including but not limited to ducts, anchorage assemblies and grout used for pressure grouting ducts.

For cast-in-place prestressed concrete, the term “member” as used in this Specification shall be considered to mean the concrete which is to be prestressed.

When members are to be constructed with part of the reinforcement pretensioned and part post-tensioned the applicable requirements of this Specification shall apply to each method.

4.1.2 Details of Design

When the prestressing work is not fully detailed on the Drawings, the Contractor shall determine the details or type of prestressing system for use and select materials and details conforming to these Specifications as needed to satisfy the prestressing requirements specified. The system selected shall provide the magnitude and distribution of prestressing force and ultimate strength required by the Drawings without exceeding allowable temporary stresses. Unless otherwise shown on the Drawings, all design procedures, coefficients and allowable stresses, friction and prestress losses as well as tendon spacing and clearances shall be in accordance with the BS 5400.

When the effective or working force or stress is shown on the Drawings, unless stated otherwise it shall be considered to be the force or stress remaining in the prestressing steel after all losses, including creep and shrinkage of concrete, elastic shortening of concrete, relaxation of steel, friction and take-up or seating of anchorages, and all other losses peculiar to the method or system of prestressing. When the jacking force is shown on the Drawings, unless stated otherwise it shall be considered to be the force applied to the tendon prior to anchorage and the occurrence of any losses, including the anchor set loss.

4.2 SUPPLEMENTARY DRAWINGS

4.2.1 Working Drawings


Bridge Works

RI4326-D017-R3-0029 16 of 82 18 October 2007

Prior to commencement of work, the Contractor shall prepare and submit to the Engineer working drawings of the prestressing system proposed for use. Fabrication or installation of prestressing material shall not begin until the Engineer has accpeted the drawings.

The working drawings of the prestressing system shall show complete details and substantiating calculations of the method, materials and equipment the Contractor proposes to use in the prestressing operations, including any additions or rearrangement of reinforcing steel and any revision in dimensions from that shown on the Drawings. Such details shall outline the method and sequence of stressing and shall include complete specifications and details of the prestressing steel and anchoring devices, working stresses, anchoring stresses, tendon elongations, type of ducts, and all other data pertaining to the prestressing operation, including the proposed arrangement of the prestressing steel in the members.

Working drawings shall be submitted sufficiently in advance of the start of the affected work to allow time for review by the Engineer and correction by the Contractor of the drawings without delaying the work.

4.2.2 Composite Placing Drawings

When required by the Engineer, in addition to all required working drawings, the Contractor shall prepare composite placing drawings to scale and in sufficient detail to show the relative positions of all items that are to be embedded in the concrete, and their embedment depth, for the portions of the structure that are to be prestressed. Such embedded items include the prestressing ducts, vents, anchorage reinforcement and hardware, reinforcing steel, anchor bolts, earthquake restrainers, deck joint seal assemblies, drainage systems, utility conduits and other such items. Such drawings shall be adequate to ensure that there will be no conflict between the planned positions of any embedded items and that concrete cover will be adequate. If during the preparation of such drawings conflicts are discovered, the Contractor shall revise his working drawings for one or more of the embedded items or propose changes in the dimensions of the work as necessary to eliminate the conflicts or provide proper cover. Any such revisions shall be submitted for review by the Engineer before work on any affected item is started. All costs involved with the preparation of such drawings and with making the necessary modifications to the work resulting therefrom shall be borne by the Contractor.

4.3 MATERIALS

4.3.1 Prestressing Steel and Anchorages

Prestressing reinforcement shall be high-strength seven-wire strand, high strength steel wire, or high strength alloy bars of the grade and type called for on the Drawings or in the Specifications and shall conform to the requirements of the following specifications:

- Strands


Bridge Works

RI4326-D017-R3-0029 17 of 82 18 October 2007

a) Strands shall be uncoated seven wire strands complying with the requirements of AASHTO M203 (ASTM A416) Supplement S1 (low relaxation) or Stress relived seven wire low relaxation super stabilised strands complying with BS 5896 as shown on the Drawings and as acceptable to the Engineer. Prestressing strand, however manufactured, shall be in coils of sufficiently large diameter to ensure that the strand pays off straight.

- Steel Wire

b) Steel wire shall be uncoated stress-relieved steel wire complying with the requirements of AASHTO M204 (ASTM A421) or BS 5896. Unless otherwise agreed by the Engineer low relaxation and normal relaxation wire shall be in coils of sufficiently large diameter to ensure that the wire pays off straight.

- Bars

c) Bars shall be uncoated high strength bars complying with the requirements of AASHTO M275 (ASTM A722). Bars with greater minimum ultimate strength, but otherwise produced and tested in accordance with AASHTO M275 (ASTM A722) may be used provided they have no properties making them less satisfactory than the specified material, subject to the agreement of the Engineer. Prestressing bars as delivered shall be straight.

- Post-tensioning Anchorages and Coupler

d) Anchorages shall be cast units and assemblies that are standard with the prestressing manufacturer’s system and agreed with the Engineer.

e) All anchorages and couplers shall develop at least 95 percent of the minimum specified ultimate strength of the prestressing steel, when tested in an unbonded state, without exceeding anticipated set. The coupling of tendons shall not reduce the elongation at rupture below the requirements of the tendon itself. Couplers and/or coupler components shall be enclosed in housing long enough to permit the necessary movements. Couplers for tendons shall be used only at locations specifically indicated and/or agreed by the Engineer. Couplers shall not be used at points of sharp tendon curvature.

f) Anchorages shall be tested in accordance with BS 4447, AASHTO LRFD Design and construction specification. Proprietary anchorages shall be handled and used strictly in accordance with the manufacturer’s instructions and recommendations. All anchorage devices shall satisfy requirements specified in articles 5.10.9.7.2 and / or 5.10.9.7.3 of AASHTO LRFD Bridge Design Specifications and article 10.3.2.3 of AASHTO Bridge Construction Specifications. Equivalent acceptance tests can be acceptable provided the procedure is generally similar to that specified in AASHTO.

- Bonded Systems


Bridge Works

RI4326-D017-R3-0029 18 of 82 18 October 2007

g) Bond transfer lengths between anchorages and the zone where full prestressing force is required under service and ultimate loads shall normally be sufficient to develop the minimum specified ultimate strength of the prestressing steel. When anchorages or couplers are located at critical sections under ultimate load, the ultimate strength required of the bonded tendons shall not exceed the ultimate capacity of the tendon assembly, including the anchorage or coupler, tested in an unbonded state.

h) Housing shall be designed so that complete grouting of all of the coupler components will be accomplished during grouting of tendons.

- Unbonded System

i) For unbonded tendons, a dynamic test shall be performed on a representative anchorage and coupler specimen and the tendon shall withstand, without failure, 500,000 cycles from 60 percent to 66 percent of its minimum specified ultimate strength, and also 50 cycles from 40 percent to 80 percent of its minimum specified ultimate strength. The period of each cycle involves the change from the lower stress level to the upper stress level and back to the lower. The specimen used for the second dynamic test need not be the same used for the first dynamic test. Systems utilising multiple strands, wires, or bars may be tested utilizing a test tendon of smaller capacity than the full size tendon. The test tendon shall duplicate the behaviour of the full size tendon and generally shall not have less than 10 percent of the capacity of the full size tendon. Dynamic tests are not require on bonded tendons, unless the anchorage is located or used in such manner that repeated load applications can be expected on the anchorage.

j) Anchorages for unbonded tendons shall not cause a reduction in the total elongation under ultimate load of the tendon to less than 2 percent measured in a minimum gauge length of 3 metres.

k) All the coupling components shall be completely protected with an agreed coating material prior to final encasement in concrete.

- Identification and Testing

l) All wire, strand or bars to be shipped to the site shall be assigned a lot number and tagged for identification purposes. Anchorage assemblies to be shipped shall be likewise identified. Each cable shall be tagged with its number from which the coil numbers of the steel used can be identified.

m) Cables shall not be kinked or twisted. Individual wires and strands of which extensions are to be measured shall be readily identifiable at each end of the member. No strand that has come unravelled shall be used.

n) Each lot of wire or bars and each reel of strand reinforcement shall be accompanied by a manufacturer’s certificate of compliance, a mill certificate, and


Bridge Works

RI4326-D017-R3-0029 19 of 82 18 October 2007

a test report. The mill certificate and test report shall include the chemical composition (not required for strand), cross-sectional area, yield and ultimate strengths, elongation at rupture, modulus or elasticity, and the stress strain curve for the actual prestressing steel intended for use. All values certified shall be based on test values and nominal sectional area of the material being certified.

o) The Contractor shall furnish to the Engineer for verification testing the samples described in the following sub-articles selected from each lot. If ordered by the Engineer, the selection of samples shall be made at the manufacturer’s plant by the Inspector.

p) All samples submitted shall be representative of the lot to be furnished and, in the case of wire or strand, shall be taken from the same master roll.

q) The actual strength of the prestressing steel shall not be less than specified by the applicable British or ASTM Standard, and shall be determined by tests of representative samples of the tendon material in conformance with the appropriate Standards.

r) If it is proposed to use super strand complying with BS 5896:1980 Table 6 or other than the lowest strength 3, 4, 5, 6 or 7mm diameter wires complying with BS 5896: 1980 Tables 4 and 5, reels will only be accepted if both the breaking load and the 0.1% proof load of the sample exceeds the specified characteristic loads given in the above Tables 4 or 6. In the case of Table 5 this requirement shall apply to the breaking load and the load at 1% elongation.

s) All of the materials specified for testing shall be furnished free of cost and shall be delivered in time for tests to be made well in advance of anticipated time of use.

- Pre-tensioning Tendon Samples

t) For pretensioned strands, one sample at least 2.1 metres long shall be furnished in accordance with the requirements of paragraph 9.1 of AASHTO M203 (ASTM A 416M).

- Post- tensioning Tendon Samples

u) The following lengths shall be furnished for each 20 ton, or portion thereof, lot of material used in the work.

- For wires requiring heading: 1.5 metres. - For wires not requiring heading: sufficient length to make up one parallel-lay cable 1.5 metres long consisting of the same number of wires as the cable to be furnished. - For strand to be furnished with fittings: 1.5 metres between near ends of fittings. - For bars to be furnished with threaded ends and nuts: 1.5 metres between threads at ends.

- Anchorage Assemblies and Couplers


Bridge Works

RI4326-D017-R3-0029 20 of 82 18 October 2007

v) The Contractor shall furnish for testing, one specimen of each size of prestressing tendon, including couplings, of the selected type, with end fittings and anchorage assembly attached, for strength tests only. These specimens shall be 1.5m in clear length, measured between ends of fittings. If the results of the test indicate the necessity of check tests, additional specimens shall be furnished without cost.

w) When dynamic testing is required, the Contractor shall perform the testing and shall furnish certified copies of test results that indicate conformance with the specified requirements prior to installation of anchorages or couplers.

x) For prestressing systems previously tested and approved on projects having the same tendon configuration, the Engineer may not require complete tendon samples provided there is no change in the material, design, or details previously approved. Shop drawings or prestressing details shall identify the project on which approval was obtained, otherwise testing shall be conducted.

- Protection of Prestressing Steel

y) All prestressing steel shall be protected against physical damage work hardening or heating and rust or other results of corrosion at all times from manufacture to grouting or encasing in concrete. Prestressing steel shall also be free of deleterious material such as grease, oil, wax or paint. Prestressing steel that has sustained physical damage at any time shall be rejected. The development of pitting or other results of corrosion, other than rust stain, shall be cause for rejection.

z) All prestressing steel shall be stored clear of the ground and be protected from the weather, from splashes from any other materials and from splashes from the cutting operation of an oxy-acetylene torch, or arc welding activity in the vicinity. In no circumstances shall prestressing steel after manufacture be subjected to any welding operation, or heat treatment or metallic coating such as galvanising. This does not preclude cutting as described in 4.5.1.

aa) Prestressing steel shall be packaged in containers or shipping forms for the protection of the strand against physical damage and corrosion during shipping and storage. A corrosion inhibitor that prevents rust or other results of corrosion shall be placed in the package or form, or shall be incorporated in a corrosion inhibitor carrier type packaging material, or when permitted by the Engineer, may be applied directly to the steel. The corrosion inhibitor shall have no deleterious effect on the steel or concrete or bond strength of steel to concrete or grout. Packaging or forms damaged from any cause shall be immediately replaced or restored to original condition.

bb) The shipping package or form shall be clearly marked with a statement that the package contains high-strength prestressing steel, and the type of corrosion inhibitor used, including the date packaged.


Bridge Works

RI4326-D017-R3-0029 21 of 82 18 October 2007

cc) All anchorages, end fittings, couplers, and exposed tendons, which will not be encased in concrete or grout in the completed work, shall be permanently protected against corrosion.

4.3.2 Corrosion Protection

Corrosion Protection shall consist of a vapour phase inhibitor (VP) powder conforming to the provisions of U.S. Federal Specification MIL-P-3420 or as otherwise agreed by the Engineer. When agreed, water-soluble oil may be used on tendons as a corrosion protection.

4.3.3 Ducts

The system of ducts, duct connectors, grouting connections, vents, vent connectors, drains, transition to anchorages and caps for anchors shall form a complete encapsulation for the tendon which is resistant to ingress of air and water. Ducts shall be of proven corrosion resistant durable material. Ducting which may degrade or corrode during the expected life of the structure shall not be permitted. The system shall be fully compatible with the prestressing anchorages, couplers and other details. Where ducts are non-conductive, metal parts of the anchorages shall be electrically bonded to the adjacent reinforcement at each end of the tendon and electrical continuity of the structure over the length of the tendon shall be confirmed by testing.

Galvanised steel ducts shall have a minimum wall thickness of 0.6mm.

Polyethylene duct shall not be used when the radius of curvature of the tendon is less than 9 metres.

Semi-rigid polyethylene ducts for use where completely embedded in concrete shall be corrugated with minimum material thickness of 1.27 mm ± 0.25mm. Such ducts shall have a white coating on the outside, or shall be of white material with ultraviolet stabilizers added.

Rigid polyethylene ducts for use where the tendon is not embedded in concrete shall be rigid pipe manufactured in accordance with ASTM D2447, ASTM F714, ASTM D2239, or ASTM D30. For external applications, such duct shall have an external diameter to wall thickness ratio of 21 or less.

For applications where polyethylene duct is exposed to sunlight or ultraviolet light, carbon black shall be incorporated into the polyethylene pipe resin in such amount to provide resistance to ultraviolet degradation in accordance with ASTM D1248.

- Duct Area

a) The inside diameter of ducts shall be at least 6mm larger than the nominal diameter of single wire, bar or strand tendons, or in the case of multiple wire, bar or strand tendons, the inside cross-sectional area of the sheathing shall be at least two times the net area of the prestressing steel. When tendons are to be placed by the pull through method, the duct area shall be at least 2.5 times the net area of the prestressing steel.


Bridge Works

RI4326-D017-R3-0029 22 of 82 18 October 2007

- Duct Fittings

b) Coupling and transition fittings for ducts formed by sheathing shall be of either ferrous metal or polyethylene, and shall be cement paste intrusion proof and of sufficient strength to prevent distortion or displacement of the ducts during concrete placement.

c) All ducts or anchorage assemblies shall be provided with pipes or other suitable connections at each end of the duct for the injection of grout after prestressing. As a specified in Clause 4.1.1, ducts shall also be provided with ports for venting or grouting at high points and for draining at intermediate low points.

d) Vent and drainpipes shall be 13mm minimum diameter standard pipe or suitable plastic pipe. Connection to ducts shall be made with metallic or plastic structural fasteners. The vents and drains shall be mortar tight, taped as necessary, and shall provide means for injection of grout through the vents and for sealing to prevent leakage of grout.

4.4 PLACEMENT OF DUCTS AND STEEL

4.4.1 Placement of Ducts

Internal and external surfaces of ducts shall be clean and free from pitting at the time of incorporation in the work.

Ducts shall be rigidly supported at the proper locations in the forms by ties to reinforcing steel that are adequate to prevent displacement during concrete placement. Supplementary support bars shall be used where needed to maintain proper alignment of the duct. Hold down ties to the forms shall be used when the buoyancy of the ducts in the fluid concrete would lift the reinforcing steel. The tolerance in location of the centreline of the duct shall be 5mm.

Joints between sections of duct shall be coupled with positive connections that do not result in angle changes at the joints and will prevent the intrusion of cement paste. After placing of ducts, reinforcement and forming is complete, an inspection shall be made to locate possible duct damage.

All unintentional holes or openings in the duct must be repaired prior to concrete placing.

Grout openings and vents must be securely anchored to the duct and to either the forms or to reinforcing steel to prevent displacement during concrete placing operations.

After installation in the forms, the ends of ducts shall at all times are covered as necessary to prevent the entry of water or debris.

- Vents and Drains

a) All ducts for continuous structures shall be vented at the high points of the duct profile, except where the curvature is small, as in continuous slabs, and at


Bridge Works

RI4326-D017-R3-0029 23 of 82 18 October 2007

additional locations as shown on the plans. Drains shall also be installed at low point in ducts where needed to prevent the accumulation of water and shall remain open until grouting is started.

b) The ends of vents and drains shall be removed 25mm below the surface of the concrete after grouting has been completed, and the void filled with mortar.

4.4.2 Placement of Prestressing Steel

- Placement for Pretensioning

a) Prestressing steel shall be accurately installed in the forms and held in place by the stressing jack or temporary anchors and when tendons are to be draped, by hold-down devices. The hold-down devices used at all points of change in slope of tendon trajectory shall be of an agreed low-friction type.

- Placement for Post-Tensioning

b) All prestressing steel pre-assembled in ducts and installed prior to the placement of concrete shall be accurately placed and held in position during concrete placement. Pre-installing of tendons shall be permitted only when the total length of tendons does not exceed 35m so that during concrete initial setting period the tendon can be moved to ensure that there is no concrete blockage inside the duct and tendons will be free to move when stressing.

c) When the prestressing steel is installed after the concrete has been placed, the Contractor shall demonstrate to the satisfaction of the Engineer that the ducts are free of water and debris immediately prior to installation of the steel. The total number of strands in an individual tendon may be pulled into the duct as a unit, or the individual strand may be pulled or pushed through the duct.

d) Anchorage devices or block-out templates for anchorages shall be set and held so that the axis of the tendon and anchor plates is normal in all directions to the tendon.

e) The prestressing steel shall be distributed so that the force in each girder stem is equal or as required by the plans, except as provided herein. For box girders with more than two girder stems, at the Contractor’s option, the prestressing force may vary up to 5 percent from the theoretical required force per girder stem provided the required total force in the superstructure is obtained and the force is distributed symmetrically about the centreline of the typical section.

- Protection of Steel after Installation

f) Prestressing steel installation in members prior to placing and curing of the concrete, or installed in the duct but not grouted within the time limit specified below, shall be continuously protected against rust or other corrosion by means of a corrosion protection placed in the ducts or directly applied to the steel. The prestressing steel shall be so protected until grouted or encased in concrete.


Bridge Works

RI4326-D017-R3-0029 24 of 82 18 October 2007

Prestressing steel installed and tensioned in members after placing and curing of the concrete and grouted within the time limit specified below will not require the use of a corrosion protection described here in and rust which may form during the interval between tendon installation and grouting will not be cause for rejection of the steel.

g) The permissible interval between tendon installation and grouting without use of a corrosion protection for various exposure conditions shall be as follows:

Table 4.1: Maximum Period for Leaving Tendons Ungrouted

Atmospheric Conditions Permitted Maximum Period Very Damp Atmosphere or over saltwater (Humidity > 70%)

7 days

Moderate Atmosphere (Humidity from 40% to 70%)

15 days

Very Dry Atmosphere (Humidity < 40%)

20 days

h) After tendons are placed in ducts, the openings at the ends of the ducts shall be

sealed to prevent entry of moisture.

i) When steam curing is used, steel for post-tensioning shall not be installed until the steam curing is completed.

j) Whenever electric welding is performed on or near members containing prestressing steel, the welding ground shall be attached directly to the steel being welded. All prestressing steel and hardware shall be protected from weld spatter or other damage.

4.5 TENSIONING

4.5.1 General Tensioning Requirements

Prestressing steel shall be tensioned by hydraulic jacks so as to produce the forces shown on the plans or on the submitted working drawing with appropriate allowances for all losses. For post-tensioned work the losses shall also include the anchor set loss appropriate for the anchorage system employed.

For pre-tensioned members, the strand jacking stress shall not exceed 80% of the minimum ultimate tensile strength of the prestressing steel.

For post-tensioned members, the strand stress prior to seating (Jacking stress) and the stress in the steel after seating shall not exceed the values allowed in AASHTO LRFD Bridge Design Specification Article 5.9.3.


Bridge Works

RI4326-D017-R3-0029 25 of 82 18 October 2007

The method of tensioning employed shall be one of the following as specified or agreed:

- Pretensioning; in which the prestressing strand or tendons are stressed prior to being embedded in the concrete placed for the member. After the concrete has attained the required strength, the prestressing force is released from the external anchorages and transferred by bond into the concrete.

- Post-tensioning; in which the reinforcing tendons are installed in voids or ducts within the concrete and are stressed and anchored against the concrete after the development of the required concrete strength. As a final operation under this method the voids or ducts are pressure-grouted.

- Combined Method; in which part of the reinforcement is pretensioned and part post-tensioned. Under this method all applicable requirements for pretensioning and for post-tensioning shall apply to the respective reinforcing elements using these methods.

- Concrete Strength

a) Prestressing forces shall not be applied or transferred to the concrete until the concrete has attained the strength specified for initial stressing. The Contractor shall cast and test sufficient cubes to demonstrate this to the satisfaction of the Engineer. In addition, cast-in- place concrete for other than segmentally constructed bridges shall not be post-tensioned until at least 10 days after the last concrete has been placed in the member to be post-tensioned.

- Prestressing Equipment

b) Tendons shall be safely and securely attached to tensioning jacks. Hydraulic jacks used to stress tendons shall be capable of imposing a controlled total force gradually so that no dangerous secondary stresses are induced in the tendons, anchorage or concrete; they shall be capable of providing and sustaining the necessary forces and shall be equipped with either a pressure gauge or a load cell for determining the jacking stress. The jacking system shall provide an independent means by which the tendon elongation can be measured. The pressure gauge shall have an accurately reading dial at least 150mm in diameter or a digital display, and each jack and its gauge shall be calibrated as a unit with the cylinder extension in the approximate position that it will be at final jacking force, and shall be accompanied by a certified calibration chart or curve. The load cell shall be calibrated to an accuracy within ± 2% and checked at intervals to the satisfaction of the Engineer; it shall be provided with an indicator by means of which the prestressing force in the tendon may be determined. The range of the load cell shall be such that the lower 10 percent of the manufacturer’s rated capacity will not be used in determining the jacking stress. When agreed with the Engineer, calibrated proving rings may be used in lieu of load cells.

c) Master gauges shall be supplied on site during the prestressing operations of the project for verifying pressure gauge readings.


Bridge Works

RI4326-D017-R3-0029 26 of 82 18 October 2007

d) Re-calibration of gauges shall be repeated at least annually and whenever gauge pressures and elongations indicate materially different stresses.

e) All cutting of wire, strand or bar shall be carried out using either:

- a high-speed abrasive cutting wheel or friction saw at not less than one diameter from the anchor, or any other mechanical method agreed by the Engineer; or - an oxy-acetylene cutting flame, using excess oxygen to ensure a cutting rather than a melting action, not less than 75mm from the anchor. The temperature of the tendon adjacent to the anchor shall not be greater than 200°C. Care shall be taken that neither the flame nor splashes come into contact with the anchorages or tendons.

- Sequence of Stressing

f) When the sequence of stressing individual tendons is not otherwise specified the stressing of post-tensioning tendons and the release of pre-tensioned tendons shall be done in a sequence that produces a minimum of eccentric force in the member.

- Measurement of Stress

g) A record of gauge pressures and tendon elongations for each tendon shall be provided by the Contractor for review and acceptance by the Engineer. Elongations shall be measured to an accuracy of 1mm. Stressing tails of post-tensioned tendons shall not be cut off until the stressing records have been accepted. A facility to measure any movement of the tendon in the gripping devices shall also be provided.

h) All tendons shall be tensioned to a preliminary force as necessary to eliminate any take-up in the tensioning system before elongation readings are started. This preliminary force shall be between 5 and 25 percent of the final jacking force. The initial force shall be measured by a dynamometer or by other method agreed with the Engineer, so that its amount can be used as a check against elongation as computed and as measured. Each strand shall be marked prior to final stressing to permit measurement of elongation and to ensure that all anchor wedges set properly.

4.5.2 Pre-tensioning Method Requirements

Stressing shall be accomplished by either single strand stressing or multiple strand stressing. The amount of stress to be given each strand shall be as shown in the drawings or the working drawings.

All strand to be stressed in a group (multiple strand stressing) shall be brought to a uniform initial tension prior to being given their full pre-tensioning. The amount of the initial tensioning force shall be within the range specified in 4.5.1 and shall be the minimum required to eliminate all slack and to equalise the stresses in the tendons as determined by the Engineer.


Bridge Works

RI4326-D017-R3-0029 27 of 82 18 October 2007

The amount of this force will be influenced by the length of the casting bed and the size and number of tendons in the group to be tensioned.

When straight tendons are used in the long-line method of pretensioning, sufficient locator plates shall be distributed throughout the length of the bed to ensure that the wires or strands are maintained in their proper position during concreting. Where a number of units are made in line, they shall be free to slide in the direction of their length and thus permit transfer of the prestressing force to the concrete along the whole line.

In the individual mould system, the moulds shall be sufficiently rigid to provide the reaction to the prestressing force without distortion.

Draped pretensioned tendons shall either be tensioned partially by jacking at the end of the bed and partially by uplifting or depressing tendons, or they shall be tensioned entirely by jacking, with the tendons being held in their draped positions by means of rollers, pins or other agreed methods during the jacking operation.

Agreed low-friction devices shall be used at all points of change in slope of tendon trajectory when tensioning draped pretensioned strands, regardless of the tensioning method used. For single tendons the deflector in contact with the tendon shall have a radius of not less than 5 times the tendon diameter for wire or 10 times the tendon diameter for strand, and the total angle of deflection shall not exceed 15°.

If the load for a draped strand, as determined by elongation measurements, is more than 5 percent less than that indicated by the jack gauges, the strand shall be tensioned from both ends of the bed and the load as computed from the sum of elongation at both ends shall agree within 5 percent of that indicated by the jack gauges.

When directed by the Engineer, prestressing steel strands in pretensioned members, if tensioned individually, shall be checked by the Contractor for loss of prestress not more than 3 hours prior to placing concrete for the members. The method and equipment for checking the loss of prestress shall be subject to agreement by the Engineer. All strands that show a loss of prestress in excess of 3 percent shall be re-tensioned to the original computed jacking stress.

Stress on all strands including hold down/hold up forces shall be maintained between anchorages until the concrete has reached the compressive strength required at time of transfer of stress to concrete. Transfer of stress shall take place slowly to minimise shock.

When prestressing steel in pretensioned members is tensioned at a temperature more than 14°C lower than the estimated temperature of the concrete and the prestressing steel at the time of initial set of the concrete, the calculated elongation of the prestressing steel shall be increased to compensate for the loss in stress, due to the change in temperature, but in no case shall the jacking stress exceed 80 percent of the specified minimum ultimate tensile strength of the prestressing steel.

Strand splicing methods and devices shall be agreed by the Engineer. When single strand jacking is use, only one splice per strand will be permitted. When multi-strand jacking is used,


Bridge Works

RI4326-D017-R3-0029 28 of 82 18 October 2007

either all strands shall be spliced or no more than 10 percent of the strands shall be spliced. Spliced strands shall be similar in physical properties, from the same source, and shall have the same “twist” or “lay”. All splices shall be located outside of the prestressed units.

Side and flange forms that restrain deflection shall be removed before release of pretensioning reinforcement.

Except when otherwise shown on the Drawings, all pretensioned prestressing strands shall be cut off flush with the end of the member and the exposed ends of the strand and a 1 inch strip of adjoining concrete shall be cleaned and painted. Cleaning shall be by wire brushing or abrasive blast cleaning to remove all dirt and residue that is not firmly bonded to the metal or concrete surfaces. The surfaces shall be coated with one thick coat of zinc-rich paint conforming to the requirements of Federal Specification TT-P-641. The paint shall be thoroughly mixed at the time of application, and shall be worked into any voids in the strands.

4.5.3 Post-Tensioning Method Requirements

Prior to post-tensioning any member, the Contractor shall demonstrate to the satisfaction of the Engineer that the prestressing steel is free and unbonded in the duct.

All strands in each tendon, except for those in flat ducts with not more than four strands, shall be stressed simultaneously with a multi-strand jack. Tensioning shall be accomplished so as to provide the forces and elongations specified in Section 4.5.1. Except as provided herein or when shown on the plans or on the submitted working drawings, tendons in continuous post-tensioned members shall be tensioned by jacking at each end of the tendon. For straight tendons and when one end stressing is shown on the plans, tensioning may be performed by jacking from one end or both ends of the tendon at the option of the Contractor.

All post-tensioning shall be by means of hydraulic jacks equipped with accurate reading calibrated hydraulic pressure gauges to permit the stress in the prestressing steel to be computed at any time. A certified calibration curve shall be submitted for each jacking system. In the event inconsistencies occur between the measured elongation and the jack gauge reading, the jack gauge shall be immediately be recalibrated. In the event still further discrepancies occur, the cause shall be determined and reported to the Engineer. An agreement within five percent shall be satisfactory.

Deflectors in contact with tendons shall have a radius of not less than 50 times the diameter of the tendon, and the total angle of deflection shall not exceed 15° unless otherwise agreed by the Engineer.

Stressing shall continue until the required extension and tendon load are reached or are accepted by the Engineer. Elongation is the preferred method of stress determination wherever possible. The tendons shall be tensioned to the total forces shown on the drawings.

Elongation shall be measured to an accuracy of 1mm. Elongation tolerances for individual tendons, based on agreed and agreed friction coefficients (established through Friction Tests) and material properties determined from laboratory tests, shall be within ± 7% of the


Bridge Works

RI4326-D017-R3-0029 29 of 82 18 October 2007

theoretical value. The Contractor shall submit elongation calculations to the Engineer for acceptance prior to commencing prestressing work. These elongations should be based on actual area and Elastic modulus values of the strands making a single Tendon; in case of a single tendon made-up of more than one prestressing steel coil, weighted average values of strand areas and Elastic modulus shall be used in the calculations.

After the tendons have been anchored, the force exerted by the tensioning apparatus shall be decreased gradually and steadily so as to avoid shock to the tendon or the anchorage. Full records shall be kept of all tensioning operations, including the measured extensions, pressure-gauge or load-cell readings, and the amount of draw-in at each anchorage. Copies of these records shall be supplied to the Engineer within 24 hours of each tensioning operation.

Unless otherwise agreed by the Engineer tendons shall not be cut less than 3 days after grouting.

- Friction Test

a) The design is based on friction losses estimated on the basis of friction and wobble coefficients as shown on the Drawings. Total friction losses shall be estimated by carrying out Friction Test on one tendon for each tendon configuration at the very start of the post-tensioning to check and compare with that obtained using theoretical coefficient values from the Contract drawings. In case the friction losses in tests exceed the computed losses, all wires shall be relieved and lubricated using water-soluble oil and re-tensioned. Values of friction and wobble coefficients obtained in Friction Test shall be used for the calculation of theoretical elongations.

4.6 GROUTING

4.6.1 General

The Contractor shall undertake grout trials in accordance with the details described in Section 4.6.11. The trials are required to demonstrate that the grouting methods and procedures proposed by the Contractor will ensure that grout completely fills the ducts and surrounds the prestressing steel.

The Contractor shall submit to the Engineer at least 4 weeks before on-site trials a detailed method statement covering proposed materials, duct, anchorage and vent arrangements, personnel, equipment grouting procedures and quality control.

4.6.2 Grout Materials

The properties of the grout, made with the materials and using the plant and personnel proposed for use on site, shall be assessed for suitability for the intended purpose sufficiently


Bridge Works

RI4326-D017-R3-0029 30 of 82 18 October 2007

in advance of grouting operations to enable adjustments to be made in use of materials or plant or personnel. All retrials shall be at the Contractor’s expense.

The materials assessment shall consist of the preparation of the grout, made with the materials and using the plant and personnel proposed for use on site, and the testing of it in accordance with Section 4.6.8. The preparation shall be carried out under conditions of temperature expected on site. If grouting operations are likely to cover different seasons, the assessment shall include the range of expected temperatures.

The sources of materials and procedures agreed as a result of satisfactory trials shall not be departed from without the written consent of the Engineer.

Unless otherwise instructed or agreed by the Engineer as a result of grouting trials, the grout shall consist only of Portland cement complying with BS12 Class 42.5 N, admixtures complying with Section 4.6.10 and water complying with BS3148.

The age, chemical composition, fineness and temperature of the cement shall be subject to close control.

The materials used shall be such that the chloride ion content of the grout shall not exceed 0.1% chlorides by mass of the cement.

4.6.3 Ducts

The system of ducts, duct connectors grouting connections, vents, vent connections, drains, transitions to anchorage and caps for anchorages shall form a complete air and water tight encapsulation for the tendons. Ducts shall be of an electrically non conductive, corrosion resistant durable material such as high density polyethylene or polypropylene. The system shall be fully compatible with the prestressing anchorages. The encapsulation shall be pressure tested before concreting to 0.1N/mm2 to demonstrate that the system is undamaged and has been correctly assembled. As a minimum, the test shall equal the results of experimental testing carried out by the manufacturer on proven systems.

The Contractor shall provide evidence of testing that the encapsulation remains intact after tensioning of the tendons, that the wall thickness of ducts after tensioning is not less than 1.5mm, and that the duct shall transmit full bond strength from the tendons to the surrounding concrete over a length no greater than 40 duct diameters.

Air vents of at least 25mm internal diameter shall be provided at the anchorages and in the ducts at troughs and crests and 400mm beyond each intermediate crest in the direction of grout flow, and elsewhere as required by the Engineer. The maximum spacing of vents shall be 15m. The vent size and spacing may be varied if trials demonstrate the suitability of alternatives. The vents shall be rigidly connected to the ducts, and holes in the ducts shall be of the same diameter as the vents and be formed before pressure testing. All ducts shall be kept free from standing water at all times and shall be thoroughly clean before grouting. All anchorages shall be sealed by caps and fitted with grouting connections and vents. Sealing of anchorages shall permit the flow of grout through the anchor head.


Bridge Works

RI4326-D017-R3-0029 31 of 82 18 October 2007

Air vents on each tendon shall be identified by labelling and shall be protected against damage at all times.

Air vents at high points shall extend to a minimum of 500mm above the highest point on the duct profile.

4.6.4 Grouting Equipment

Grouting equipment shall consist of mixer, a storage reservoir and a pump with all the necessary connection hoses, valves, measuring devices for water, cement and admixtures and testing equipment.

The mixing equipment shall be capable of producing a grout of homogeneous consistency and shall be capable of providing a continuous supply to the injection equipment.

The capacity of the equipment shall be such that the duct can be filled and vented without interruption and at the required rate of injection.

The injection equipment shall be capable of continuous operation with little variation of pressure and shall include a system for re-circulating the grout while actual grouting is not in progress.

The equipment shall have a constant delivery pressure of less than 1 N/mm2, it shall be equipped with a pressure gauge and shall prevent pressures above 2 N/mm2. All piping to the grout pump shall have a minimum number of bends, valves and changes in diameter and shall incorporate a sampling Tee with stop cock.

The equipment shall be capable of maintaining pressure on completely grouted ducts and shall be fitted with a valve that can be locked off without loss of pressure in the duct.

During the grouting operation, the Contractor shall provide adequate flushing out plant to facilitate complete removal of the grout in the event of a breakdown of the grouting equipment or other disruption before the grouting operation has been completed and shall demonstrate that this equipment is in full working order.

All equipment shall be kept free from build-up of adhering materials by washing as required.

4.6.5 Batching and Mixing of Grout

All materials shall be batched by mass except the mixing water and liquid admixtures, which may be batched, by mass or volume. The accuracy of batching shall be:

- ± 2% for cement and admixtures

- ± 1% of mixing water

of the quantities specified. The mixing water shall include the water content of liquid admixtures.


Bridge Works

RI4326-D017-R3-0029 32 of 82 18 October 2007

Depending upon environmental or materials influence (e.g. temperature, configuration of the tendon and properties of the cement used), the w/c ratio shall be kept as low as possible having regard to the required plastic properties of the grout.

The maximum w/c ratio shall be 0.40. The material shall be mixed to produce a homogeneous grout and kept in slow continuous agitation until pumped into the duct. Water shall be added to the mixer first followed by the cement and admixtures. The batch quantities of cement and admixture may be added as a whole or in part in sequence until the total quantities are added. The minimum mixing time determined from grouting trials shall be adhered to.

The temperature of freshly mixed grout shall be between 5°C and 25°C.

4.6.6 Injecting Grout

Grouting operation shall be carried out by operative with appropriate knowledge, training and proven experience in carrying out similar operations and certified under an approval scheme.

A check shall be made to ensure the ducts, vents, inlets and outlets are capable of accepting injection of the grout. This shall be done by blowing through the system with dry, oil-free air and proving each vent in turn.

Where there is water in the duct, it shall be removed. Outlets at the lowest points and dry, oil-free compressed air may be used for this purpose.

Grouting of the ducts shall be carried out as soon as is practicable after the tendons have been stressed and the Engineer’s written agreement to commence has been obtained (Ref. also Section 4.4.2.). Injection shall be continuous, and it shall be slow enough to avoid producing segregation of the grout. Unless otherwise agreed by the Engineer, grout injection shall be at the rate of between 5 and 15 metres of duct per minute as per CEB-FIP Model Code 1990. The method of injecting grout shall ensure complete filling of the ducts and complete surrounding of the steel. Grout shall be allowed to flow from each vent and the free end of the duct until its consistency is equivalent to that of the grout injected. Following this, a further 5 litres at each vent shall be vented into a clean receptacle, tested in accordance with Section 4.6.9 and then discarded. The opening shall be firmly closed. All vents shall be closed in a similar manner one after another in the direction of the flow except that at intermediate crests the vents 400mm downstream shall be closed before their associated crest vent.

The injection tubes shall be sealed off under pressure. A pressure of 0.5N/mm2 shall be maintained for at least one minute.

Grout vents at high points shall be reopened 10 minutes after completion of grouting and any escape of air, water or grout recorded and reported immediately to the Engineer. A further pumping of grout may be required at this stage to expel bleed water and/or entrapped air. This shall be carried out with only the high points open one at a time sequentially in the direction of grouting.

The filled ducts shall not be subjected to shock or vibration within 24 hours of grouting.


Bridge Works

RI4326-D017-R3-0029 33 of 82 18 October 2007

Not less than 48 hours after grouting, the level of grout in the injection and the vent tubes shall be inspected, all defective grout shall be removed from the vent and the level topped up as necessary with freshly mixed grout.

Not less than 48 hours after grouting, the end caps at anchorages shall be removed and photographic record taken, clearly identified.

If, in the opinion of the Engineer, there is cause for doubt that the ducts are completely filled with grout, the Engineer may require non-destructive testing to be carried out.

The Contractor shall keep full records of grouting for each duct including the date each duct was grouted, the proportion of the grout and any admixturs used, the pressure, details of any interruptions and topping up required, and the records shall be in accordance with the recommendations of the certification scheme. Copies of these records shall be supplied to the Engineer within 24 hours of grouting.

Grout vents shall be positively sealed to be waterproof on completion of grouting so as to maintain the encapsulation to the tendons by a means separate from the concrete waterproofing.

4.6.7 Grouting During Adverse Weather

- Hot Weather

a) Grouting in conditions where the shade air temperature exceeds 30°C will only be permitted when the Contractor’s proposals for ensuring that Grout quality will not be impaired have been accepted by the Engineer.

b) During hot weather, the Contractor shall ensure that the constituent materials of the Grout are sufficiently cool to prevent the Grout form stiffening in the interval between its discharge from the mixer and compaction in its final position. Cement shall not be allowed to come into contact with water at a temperature greater than 40°C. In all circumstances grout temperature shall not exceed 32oC during mixing or pumping.

c) Flushing of duct with cold water (complying with the requirements of Section 1.4 of Bridge Concrete Works Specification) shall be required in case the temperature of the structure exceeds 30oC. In such case when ducts are flushed with water, the Contractor shall make sure that there is no water left in the duct by opening the drains located at the low points and by blowing air through the duct. Flushing should be avoided for large size ducts where there is a risk that some water will be left inside the duct; in such cases grouting should be done when the structure is cooled down below 30oC.

d) Not withstanding the above recommendations Grouting shall not be carried out when the shade air temperature exceeds 35°C or during “ghibli” conditions.

- Cold Weather


Bridge Works

RI4326-D017-R3-0029 34 of 82 18 October 2007

e) When the ambient temperature may be expected to fall below 5°C, accurate temperature records shall be kept covering maximum and minimum air temperatures, and temperatures of the structures and adjacent to the ducts to be grouted. No materials in which frost or ice is present shall be used, and the ducts and equipment shall be completely free of frost and ice.

f) No grout shall be placed when the temperature of the structure adjacent to the ducts is below 5°C, or is likely to fall below 5°C during the following 48 hours, unless the member is heated so as to maintain the temperature of the placed grout above 5°C for at least 48 hours. Methods of heating shall be to the satisfaction of the Engineer.

g) Ducts shall not be warmed with steam.

4.6.8 Properties of Grout

- Fluidity

a) The fluidity of the grout during the injection period shall be high enough for it to be pumped effectively and adequately to fill the duct, but low enough to expel the air and any water in the sheath. When tested by the method given in Section 4.6.9, the grouts shall have the values given in Table 1. Additionally the fluidity at the duct outlets shall not exceed that of the injected grout by more than 10%.

Table 4.2: Fluidity Test Requirements

Test method

Immediately after mixing

Time(s)

At the end of the injection period subject to a min. of 30 minutes after mixing*

Time(s)

At duct outlet

Time(s)

Cone < 25 < 25 > 10 * Mixing time shall be measured from the time when all of the materials are in the mixer.

b) For grouts prepared in some mixers which have a high shear mixing action the upper limits given in Table 4.2 may be increased to 50s. The mixer and these limits shall be subject to the acceptance of the Engineer.

- Bleeding

c) The bleeding of the grout shall be sufficiently low to prevent excessive segregation and settlement of the grout materials. When tested by the method given in Section 4. 6.9, the bleeding shall be less than 2% of the initial volume of the grout and the average of four successive results shall be less than 1%. The water shall be reabsorbed by the grout during the 24 hours after mixing.

- Volume Change

d) The volume change assessed may be either an increase or decrease. When tested in accordance with the method given in Section 4. 6.9, the volume change


Bridge Works

RI4326-D017-R3-0029 35 of 82 18 October 2007

of the grout shall be within the range 0% to +5%. For grouts with expanding agents there shall be no decrease in volume.

- Strength

e) The compressive strength of 100mm cubes made of the grout shall exceed 27N/mm2 at 7 days. Cubes shall be made, cured and tested in accordance with BS 1881.

- Sieve Test

f) The grout shall contain no lumps. This shall be verified by checking the sieving the medium on the fluidity test cone.

4.6.9 The Testing of Grout

Testing shall comprise suitability testing of the materials assessment, and acceptance testing of the grouting trials and actual works operations.

Suitability testing shall wherever possible be carried out in the conditions of temperature and humidity expected on site but in the absence of this data the conditions of temperature and relative humidity at test shall be as follows:

- Temperature 20°C ± 2°C

- Relative humidity > 65%

Variation in temperature and humidity on site are likely to cause variations in the test results and shall be reported.

The temperature of the freshly mixed grout shall be given in all test reports.

- Fluidity Test

a) Principle

The fluidity of the grout, expressed in seconds, is a measure of time necessary for a stated quantity of grout to pass through the orifice of the cone, under stated conditions.

b) Apparatus

The following apparatus is required for the test: - Cone; A cone of the dimensions given in Figure 1 in the Appendix to this Specification. It shall be robust and manufactured from materials not reactive with any materials specified. A tap shall be fitted at the lower cone orifice. - Sieving medium; The sieving medium aperture shall be 1.5mm and the sieving medium shall be fitted as shown in Figure 1, and be removable. - Stopwatch; The stopwatch shall be accurate to 0.2 seconds in 60 seconds and shall show time to 0.1 seconds.

c) Test procedure

Mount the cone with its axis vertical and its largest diameter uppermost. Fix the sieving medium at the position indicated in Figure 1. During the test, prevent the cone from vibrating. Place the cylinder under the cone outlet. All surfaces of the


Bridge Works

RI4326-D017-R3-0029 36 of 82 18 October 2007

cone shall be clean and shall be dampened so that the surfaces are moist but without free water. Close the lower cone orifice. Pour the grout through the sieving medium to fill the conical section of the cone. Pouring shall be sufficiently slow to prevent the build-up of air in the grout in the cone. Open the lower cone orifice and, at the same time, start the stopwatch. Measure the time taken to the nearest 0.5s to fill the cylinder to 1 litre. The presence of lumps on the sieving medium shall be reported. For suitability testing three tests shall be carried out, the first immediately after the grout is mixed and the remaining two tests 30 minutes after the grout is mixed. The grout shall be kept agitated while awaiting testing.

d) Reporting of results

Report the time to the nearest 0.5s. Report also the presence of lumps. Report the result as the average of the times determined to the nearest 0.5 of the second and third tests, separately from the results of the first test. For acceptance testing, the test shall be performed on grout from each anchorage outlet and from the mixer at the start and end of grouting of each duct.

- Bleeding Test

e) Principle

The test consists of measuring the quantity of water remaining on the surface of the grout which has been allowed to stand protected from evaporation.

f) Apparatus

A transparent cylinder 50mm internal diameter and 200mm in height graduated in mm.

g) Test Procedure

Place the cylinder on a surface free form shocks or vibration. The grout used should be from the same batch as that used for the fluidity test. Pour grout into the cylinder to a height of approximately 150mm and seal the cylinder to prevent evaporation. Note the height to the top of the grout (h) ignoring the meniscus. After 3 hours, measure the depth of water on top of the grout (h1). After 24 hours, check whether the water has been reabsorbed. The test is carried out on one sample of grout.

h) Reporting of Results

Bleeding at the end of 3 hours is given by: h1 x 100 (%) h

where: h1 is the height in mm of water on the surface of the grout after 3 hours. h is the initial height in mm of grout The report shall state the range of air temperatures and the grout temperature at the time of test, the bleeding at 3 hours and whether the water has been reabsorbed after 24 hours. For acceptance testing, a minimum of two tests per day shall be performed.

- Volume Change Test

i) Principle


Bridge Works

RI4326-D017-R3-0029 37 of 82 18 October 2007

The volume change is measured as a percentage of the volume of grout between the start and the end of the test. The test measures mainly the volume change caused by segregation, contraction or expansion. The volume change test may be a continuation of the bleeding test.

j) Apparatus

A transparent cylinder 50mm internal diameter and 200mm in height graduated in mm.

k) Test procedure

Place the cylinder on a surface free from shocks or vibration. Fill it with grout to approximately 150mm and seal the cylinder to prevent evaporation. Note the height to the top of the grout h ignoring the meniscus. 24 hours after filling the cylinder measure the height of the grout in the cylinder (h2).

l) Reporting of results

Volume change at the end of 24 hours given by: (h2 – h) x 100%

h where: h is the initial height in mm of grout h2 is the height in mm of grout after 24 hours The report shall state the range of air temperatures during the test and the volume change. For acceptance testing the test shall be performed twice each day.

4.6.10 Admixtures

- General

a) Admixtures shall be used to achieve a low water/cement ratio and impart good fluidity, minimum bleed and volume stability or expansion to the grout to comply with Section 4.6.8 of this specification. They should be added on site during the mixing process and used in accordance with manufacturer’s recommendations.

- Types

b) Admixtures are divided into two types – expanding and non-expanding.

c) Expanding grout admixtures are supplied as powders which expand to ensure there is no decrease in the volume of grout at the end of the hardening period. Non-expanding grout admixtures are supplied in liquid or powder form.

d) Both types of grout admixture may also permit a reduction in water/cement ratio, improve fluidity, reduce bleeding and retard the set of the grout.

e) Admixtures may be used singly or in combination to obtain the required grout performance. Admixtures used in combination shall be checked for compatibility.

- Chemical Composition


Bridge Works

RI4326-D017-R3-0029 38 of 82 18 October 2007

f) Admixtures shall not contain substances in quantities, which will adversely affect the grout or the corrosion protection of the prestressing steel. Thiocyante, nitrates, formate and sulphides shall not be used in admixtures.

- Material Requirements

g) The admixture shall not segregate and shall be uniform in colour. The composition shall not change and the supplier shall operate a quality system complying with BS EN ISO 9001 or BS EN ISO 9002. Where appropriate, admixtures shall comply with BS 5075: Parts 1 and 3. Other admixtures shall be permitted provided they satisfy sections 6, 7.1 and 7.3 of BS 5075: Part 1 and full account is taken of their effects on the finished product and their fitness for purpose. Data on their suitability, including previous experience with such materials, shall be made available and records of the details and performance of such materials shall be maintained.

- Corrosion

h) Grout admixtures shall not cause the grout to promote corrosion of the prestressing steel by rusting, pitting, stress corrosion or hydrogen embrittlement.

- Dosage

i) The optimum dosage of the admixture shall be determined by trial mixes with the cement to be used in the grout. This dosage shall be expressed as percent by mass of cement. It shall be within the range recommended by the supplier and shall not exceed 5% by mass of the cement.

j) The method of measuring dosage and checking weights of pre-packed dry materials shall be agreed with the Engineer.

4.6.11 Grouting Trials

The Contractor shall provide full documentary evidence to the satisfaction of the Engineer of successful grouting trials on a similar project, using similar grout and similar equipment. Otherwise, at least 56 days before the planned commencement of fixing ducts for prestressing for the permanent works, the Contractor shall carry out full-scale grouting trials. The trial shall comprise a 25m long concrete beam 350mm wide and 1500mm deep, incorporating one tendon with a high point and a low point in a profile to be instructed by the Engineer. All relevant details of ducts, vents, duct supports, prestressing anchorages, prestressing strands, grout inlets and outlets shall be incorporated.

The tendons shall be sufficiently tensioned such that the strands within the duct take up a representative alignment. All system methods and materials are to be those proposed for the permanent works and shall have been submitted to the Engineer as part of the detailed method statement required in Section 4.6.1.

Grouting and testing shall be carried out in accordance with the Specification.


Bridge Works

RI4326-D017-R3-0029 39 of 82 18 October 2007

After 3 days the Contractor shall carefully cut and expose cross-sections and longitudinal sections of the duct and anchorages where directed by the Engineer to demonstrate that the duct is fully grouted.

A report shall be prepared by the Contractor giving full details of the trial, testing results and photographs of the cut sections.

Prestressing for the permanent works will not be permitted without the written acceptance of the Engineer to the grouting procedures and formal acceptance of the results of the grouting trial or the documentary evidence of previous grouting trials.

4.6.12 Protection of Tendons

The prestressing tendons shall be protected by cement grout within a pressure tested completely sealed encapsulation.

Metal parts of anchorages shall be electrically bonded to the adjacent reinforcement at each end of the tendon. Electrical continuity of the structure over the length of the tendon shall be tested.

4.6.13 Supervision of Prestressing Operations

Prestressing and grouting operations shall be under the charge of Supervisor with appropriate knowledge, training and experience in carrying out similar operations. That person shall be present during all procedures and shall be responsible for all safety precautions relating to the operations. The Contractor shall ensure that he is aware of the required tendon loads, order of stressing, extensions, allowance for losses and all other particulars related to the operations.

The appointment of the responsible person shall be subject to the agreement of the Engineer.

The supervisor and all operatives shall be certified under a recognised certification scheme as having the necessary qualifications.


Bridge Works

RI4326-D017-R3-0029 40 of 82 18 October 2007

APPENDIX 1


Bridge Works

RI4326-D017-R3-0029 79 of 82 18 October 2007

10 SPECIAL ITEMS

10.1 VEHICULAR PARAPET

10.1.1 General

Parapets shall be of concrete or metal or a combination of both as indicated on the drawings and shall comply with this Part.

10.1.2 Concrete Parapets

Concrete parapets shall be designed in accordance with BS 6779 Part 2:1991 and the additional requirements given in BD 52. Alternatively, Concrete Parapets designed to AASHTO Standard Specifications or AASHTO-LRFD Bridge Design Specifications will be also acceptable.

10.1.3 Metal Parapets

Metal parapets for vehicle containment shall be designed, fabricated, installed and tested in accordance with the requirements of BS 6779: Part 1 and the additional requirements given in Clause 11 below and Standard BD 52 Chapter 8.9 to 8.13 inclusive and Chapter 9.

When using BS 6779 : Part 1, the parapet group designation as give in Standard BD 52 for vehicle and vehicle pedestrian parapets shall be take to have the following equivalent level of containment as defined in BS 6779:

P1;P2(113km/h) : Normal level of containment P2 (80km/h) : Low level of containment P5 (excluding footbridges)

: Normal level of containment

P6 : High level of containment Containment level of the parapets shall be as mentioned on the drawings.

Pedestrian parapets shall be in accordance with the requirements of BS 7818.

Metal Parapets designed to AASHTO-LRFD will be considered acceptable.

10.1.4 Aesthetic Approval

The aesthetic design of metal parapets shall be agreed with the Engineer.

10.1.5 Anchorages and Attachment Systems for Metal Parapets for Vehicle Containment

The design, fabrication and installation of the anchorage and attachment system shall comply with the requirements of BS 6779 : Part 1 : 1998 and the additional requirements given in Clause 11 below.


Bridge Works

RI4326-D017-R3-0029 80 of 82 18 October 2007

The anchorages and attachment systems shall be designed to Limit State principles in accordance with Appendix B of BS 6779 : Part 1 : 1998.

Anchorages shall hold a current quality certificate from recognized establishment acceptable to the Engineer. Only anchorages so certified shall be incorporated into the Works. Anchorages in drilled holes of an expanding type shall not be used.

For anchorages in drilled holes, the hole location shall be checked to ensure that the hole will be clear of reinforcement before drilling is carried out.

Before installation of anchorages in drilled holes, the hole shall be sound, clean and dry and the tolerance of the hole shall be within the values given by the anchorage manufacturer.

Attachment systems shall be tightened to the appropriate torque.

10.1.6 Amendments and Additions to BS 6779 : Part 1: 1998

Clause 6.6.1

Insert additional sentence at end of clause as follows:

“The anchorage shall include an internally threaded component to receive the holding down bolt.”

Clause 6.6.5

End of Note 1, insert:

“The tensile strength of concrete should be ignored in the calculation.”

Clause 9.4

9.4.2.3.5 Insert additional paragraph at end of clause as follows:

“Previous Test Reports. Copies of certified reports of destructive tests on components supplied under earlier major highway contracts shall be provided.

9.4.3.2.2 Insert additional paragraph at end of clause as follows:

“(f) For all other components, including end posts, post anchorages, safety fence connections and other components: One component for each type, unless successful destructive testing has been carried out within the last 6 months on a component of that type under another contract acceptable to the Engineer.

Clause 10.1.1

Insert additional paragraph as follows:

“The designer or manufacturer shall arrange for third party certification that the new parapet design complies with the requirements of this standard. The certification shall be undertaken by a body or testing laboratory offering suitable and satisfactory evidence of technical and professional competence and independence. The Engineer is likely to require to examine the full record of testing.”


Bridge Works

RI4326-D017-R3-0029 81 of 82 18 October 2007

Annex B Clause B 2.2e delete “9.1.3.6” and insert “9.1.2.6”.

10.1.7 Bedding Mortar

Bedding mortar shall comply with the Project Concrete specifications

10.1.8 Protection Against Corrosion

Surface preparation and protection against corrosion shall comply with relevant British Standards. All steel parapets, mesh and infill panels shall be galvanized after shop fabrication. Backing materials used internally in site welded rail joints may be provided without a surface finish.

10.1.9 Inspection and Testing of Parapet Posts

The components for production posts and all completed production posts shall comply with the acceptance criteria described in Clause 27 of BS 6779 : Part 1 : 1998.

The Contractor shall only supply parapet posts of a type which have certification for static destructive testing in accordance with Clause 27 of BS 6779 : Part 1 : 1998. Test certificates shall be valid for a period of six months from the date the posts were tested and certified.

10.1.10 Site Tests on Anchorages in Drilled Holes

The Contractor shall carry out Site tests on anchorages in drilled holes. For the purpose of this sub-Clause the types of fixing referred to in Clause 1 of BS 5080: Part 1 : 1993 shall include ‘anchorages’. Where anchorages are tested they shall be loaded incrementally in tension in accordance with BS 5080 : Part 1: 1993 except that they shall be capable of resisting a test load equal to 10 per cent above the nominal tensile load to be resisted by the anchorage in lieu of testing to failure. The nominal tensile load shall be determined in accordance with the criteria given in Appendix B of BS 6779 : Part 1 : 1998. Incremental loads shall be held for not less than half a minute and the test load for not less than five minutes. Readings shall be taken immediately after applying load and at the end of the time intervals stated above.

The total movement of the anchorage shall not exceed 1.0 mm during the test. Any evidence of slip during loading up to the test load, as demonstrated by a significant change in the slope of the load/extension curve, shall constitute failure.

The Contractor shall test the anchorages at the frequency recommended by the supplier and agreed with Engineer.


Bridge Works

RI4326-D017-R3-0029 82 of 82 18 October 2007

End of Specification

prestressing works specs

Documents

system of prestressing

prestressing work

prestressing requirements

prestressing operations

particular prestressing

type of prestressing

supplementary drawings

details of design